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高精度分光を目指した CaH + の生成とトラップ

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富山大学・理 森脇喜紀

Spectroscopy of 40CaH+

thepure vibrational transition (v=0, J=0, F=1/2, M=±1/2) → (v=1, J=0, F=1/2, M=±1/2) can potentially be measured with an uncertainty of 10-16

by use of

simultaneous trapping with Ca+ ions

sympathetic cooling

quantum logic measurement

Application to the test of the time invariance of fundamental constants e.g. electron-proton mass ratio

{

P.O.Schmidt et al.

Science 309, 749(2005)

Shelkovnikov et al. PRL100, 150801 (2008)

Vibrational transition of SF6Dn/n～10-14

Kajita and Moriwaki J. Phys. B 42, 154022(2009)

- Simultaneous trapping of a 40CaH+ and a 40Ca+ in a linear trap

- Long interaction time reduces the homogeneous linewidth
- Ions in a crystal state inside a linear trap are free from Stark shift
- Some transition frequenciesof molecular ionsare free fromZeeman shift

CaH+ （v = 0, J = 0, F = 1/2, M = ±1/2）

→ （v = 1, J = 0, F = 1/2, M = ±1/2） transition

f = 42.24 THz (7.1 mm)

(1) Natural linewidth 2.5 Hz

(2) Zeeman shift (magnetic field < 1 G) < 1.3 x 10-17

(3) Stark shift induced by the trapping electric field < 10-17

(4) Electric quadrupole shift iszerobecause ofF = 1/2

(5) Stark shift induced by probe laser light is most dominant

~ 1.2 x 10-16 with saturation power (32 mW/cm2)

(1) Laser ablation of Ca containing solids

(2) Ca++H2 → CaH+ +H

Georgiadis et al. J. Chem. Phys. 92, 7060 (1988)

endothermic reaction

2.5 eV

Ca+ (4p 2P 1/2) + H2 CaH+ + H

?

To Trap

Pump laser

(397 nm)

Repump laser

(866 nm)

Hyperboloid electrodes

r0=7.5 mm

Vdc=0 V

Vac=350 V

Ω/2π=1.65 MHz

Dz=25 eV

Vdc+Vac cos Ωt

Doppler width

~2 GHz

Δr~0.45 mm

Δz~0.23 mm

T~600 K

LIF signal is proportional to the number of Ca+ ions.

With H2 buffer gas, LIF decay significantly.

Ca+ (4p2P1/2)+H2→CaH++H ?

t~11000 s

t~3600 s

Buffer gas : H2 (99.99995%)

The mass signal (m=41u) is normalized by that of m=40 u

M=41u signals appear with the laser irradiation.

With D2 buffer gas, m=42 u signals are observed.

Production of CaH+, CaD+ has been confirmed !

Without 397nm and 866nm laser, LIF decays slowly.Without 866 nm laser, LIF decays fast although the 2D3/2 state is optically pumped.

/

Ca+ (3d 2D 3/2) + H2 CaH+ + H

Photoassociated ion loss?

There have been no experimental data on CaH+.

Needs for reliable theoretical data

ab initio calculations of Ca+-H potential curves

electric energy levels, vibrational levels, Rotational constants, transition dipole moments

by M. Abe (collaborator)

Ca+2P [(4p)1] + H 2S [(1s)1]

Ca+2D [(3d)1] + H 2S [(1s)1]

Ca+2S [(4s)1] + H 2S [(1s)1]

a 4th order MBPT: Canuto et al. Phys. Rev. A. 1993.

b Two-elec. valence CI and core polarization: Boutalib et al. Chem. Phys. 1992.

31S

21S

- We proposed high precision measurements of the pure vibrational transition of 40CaH+
- production of CaH+ , CaD+ is confirmed

Future

- laser spectroscopy of CaH+

Cryogenic ion trap:

99% of CaH+ ions are localized in the (v,J)=(0,0) state at T=4 K

H2 vapor pressure ~ 10-7 Torr

- 梶田雅稔 (NICT)
- 阿部穣里(Tokyo Metropolitan Univ.)
- 松島房和, 小林かおり, 榎本勝成(富山大学)
小山達也, 中口利彦, 日比野誠(学生)